1. Field of the Invention
The present invention relates to a driving apparatus, an exposure apparatus which comprises the same, and a device fabrication method which fabricates a device using the exposure apparatus.
2. Description of the Related Art
An exposure apparatus is used in a lithography process, more particularly an exposure process to fabricate a device such as a semiconductor device. The exposure apparatus is configured to project a pattern on a mask held by a mask stage onto a wafer held by a wafer stage by using a projection optical system, and to expose the wafer.
A stage apparatus is used to hold and position the wafer and mask. The stage apparatus comprises a stage provided with a chuck which holds the wafer and mask, and a driving mechanism which drives the stage. For example, the driving mechanism can include a movable body which moves together with the stage, a guide which supports or guides the movable body, an actuator such as a linear motor which generates a driving force, and the like. The movable body can move while forming an almost constant gap with respect to the guide by a levitation force generated by an air pad and an attracting force generated by a pressurization magnet.
Conventionally, the guide is made of cast iron, and its surface is plated with nickel and phosphorus to prevent surface oxidation and increase the hardness and surface accuracy.
In an air guide mechanism, air may be shut off while the stage moves. Then, the air pad may come into contact with the guide and damage the guide. The guide may also be damaged if the stage moves with small dust or the like being present between the air pad and guide. When the metal material described above is used as the material of the guide, if the guide surface is damaged, the surface of the metal material may undesirably bulge. In this state, when the stage or the like moves along the surfaces of the respective guides, the bulge of the guide may rub against the air pad.
Consequently, the geometric accuracy of motion of the air guide mechanism may be impaired, or the dynamic characteristics of the air guide mechanism may fluctuate to considerably degrade the control performance over the moving stage. If the air guide mechanism is continuously used over a long period of time in this state, the air pad may gradually wear out until becoming critical. In an extreme case, the air pad collides against the guide to make the stage inoperable. Hence, the air guide mechanism has drawbacks regarding long-term stability.
Japanese Patent Laid-Open No. 9-5463 discloses an example in which a stage base is made of an alumina ceramic material. As the alumina ceramic material is a non-magnetic body and cannot be magnetically pressurized, it is pressurized by a vacuum pad. In an arrangement using a pressurization pad as a vacuum pad, to generate an attracting force equal to that of a pressurization magnet, the pressurization pad must have a pad area larger than the area of the pressurization magnet. Also, a vacuum air line must be formed in addition to a pressure air line. This complicates mounting on the lower surface of a fine-movement stage which forms the pad as well as pipe mounting of the entire stage apparatus. In addition, to obtain an attracting force equal to that of the pressurization magnet, high-vacuum air is needed. Therefore, a high-vacuum air line must be connected to the exposure apparatus.
Japanese Patent Laid-Open No. 2000-260691 discloses an example in which a ceramic material is sprayed onto a stage base. When using a pressurization magnet, a thin ceramic layer must be formed. If the spray ceramic layer is formed thin, however, the rigidity of an air pad slide surface cannot be maintained. If the thicknesses of the magnet pressurization surface and air pad slide surface are to be changed, the number of steps of processing the ceramic layer must be increased, leading to degradation in accuracy and an increase in cost.